text: DWV elbows are usually long-radius ("sweep") types. To reduce flow resistance and solid deposits when the direction of flow is changed, they use a shallow curve with a large radius of curvature. In addition, a well-designed system will often use two 45° elbows instead of one 90° elbow (even a sweep 90° elbow) to reduce flow disruption as much as possible.
  Central vacuum system inlet fittings are intentionally designed with a tighter curvature radius than other bends in the system. If vacuumed debris becomes stuck, it will jam at the inlet, where it is easy to find and remove.